David Robson: By any name, these are weeds

Monday

Jul 26, 2010 at 12:01 AMJul 26, 2010 at 2:20 PM

In “Romeo and Juliet,” Juliet asks, “What’s in a name? That which we call a rose by any other name would smell as sweet.” With all due apologies to Shakespeare, that which we call a “watergrass” would be just as annoying in the yard.

David Robson

In “Romeo and Juliet,” Juliet asks, “What’s in a name? That which we call a rose by any other name would smell as sweet.”

With all due apologies to Shakespeare, that which we call a “watergrass” would be just as annoying in the yard.

For years, neighbors have called across fences to each other, pointing out, “Hey, Bob. Nice stand of watergrass over there.” It’s almost a badge of shame, as homeowners cringe when their dirty little secret is exposed.

The most frustrating thing about watergrass is that there really isn’t any one plant with that name, unlike dandelion, creeping Charlie or thistle. There is a watergrass, but it’s a southern United States specimen.

In the Midwest, people use “watergrass” to describe a number of annoying summer weeds that seem to pop up overnight during the heat of summer and resist all forms of control (short of a flamethrower or nuclear smart bomb).

The only thing they have in common, besides rapid growth and an ability to thumb their collective noses at control, is that they are all grasses or grass-like.

By best accounts, there are a half-dozen plants lumped under the moniker “watergrass”: crabgrass, goosegrass, foxtail, nutsedge, quackgrass and tall fescue. All but nutsedge are true grasses.

Nutsedge looks like a grass, until you realize that the stems are triangular instead of rounded and folded. Just rub the stem with your fingers and you’ll feel three distinct sides. The color is a yellowish-green with a brown seed head that birds find as delectable as humans find chocolate.

Nutsedge, like most sedges, thrives on moisture and poor competition. You’ll find it growing mainly in the sun in areas where regular lawn grasses have thinned or are not mowed much.

The true grasses are harder to separate. They all seem to look the same: big, wide blades of grass suffocating the narrow leaves of most bluegrass and ryegrass.

Most watergrass falls into the crabgrass/foxtail/goosegrass group, composed of annual warm-season grasses that sprout each year in the spring and revel in summer’s warmth.

Most folks are familiar with foxtail as the “I-want-to-look-like-a-country-hick-so-I’ll-pull-this-grass-and-stick-the-flowering-stem-in-my-mouth.” They think crabgrass and goosegrass are low-growing species that creep along the ground. That could be a wrong assumption.

Crabgrass and goosegrass grow 3 to 4 feet tall unless mowed. Once mowed, something clicks in the prehistoric DNA of these plants, and all growth from that point forward tends to be horizontal.

But if the plants are growing someplace unimpeded — such as behind the garage or in an alley where they’re not mowed — they’ll zoom toward the sky just like any foxtail. And like foxtail, they all love moisture and high temperatures.

Crabgrass is as different from goosegrass as goosegrass is as different from foxtail.

And to compound the issue more, there are different forms of crabgrass, from hairy to smooth, and different forms of foxtail from green to yellow to giant.

Only goosegrass seems to be its own entity.

While the above three are annuals, quackgrass and tall fescues are perennials, coming back year after year. Quackgrass spreads via runners, much like creeping Charlie. Tall fescue clumps just like crabgrass but tends to be more upright than flat after mowings.

Except for tall fescue, which technically is a cool-season grass, all of the above thrive between 80 and 100 degrees, creating a dense, deep-root system to grab any drop of soil moisture they can. With cool-season grasses going dormant and barely putting up any resistance, the watergrass thugs take over.

Once the watergrasses are up, no matter what type they are, there’s not much you can do short of either living with them or killing everything off and starting over again in early September. Granted, you could forego grass and go with a patio or more ornamentals.

The best time to control the annuals is before they sprout from the ground, usually by applying a pre-emergence herbicide in the spring.

Even if you followed that course this year, the spring rains may have diluted the weedkillers, and some of the weeds could have germinated. That’s why repeat applications in wet springs are often recommended.

If you decide to use one of the products sold for summer control, remember two things.

First, follow all the directions on the label to the letter. Be aware of moisture and temperature conditions, especially daytime temperatures above 90 degrees.

Second, if you get any type of control, jump for joy. If you get little control, realize you are in the same boat as everyone else. Just try to keep it mowed so seeds don’t form for next year.

David Robson is a horticulture educator for the University of Illinois Extension. For more gardening information, go to www.extension.uiuc.edu/mg.